as long as the enclosures are the same, and subject to the same conditions it should be okay.

A good way around this is to have the thermostat probe directly on the heat tape. so it is the tape getting to the required temperature, not the substrate of one tank. Hold it against the tape with foil tape, covering the whole thing, except for the part touching the the heat tape. That way you would avoid any ambient temperatures cooling your probe, and over heating your tape.